For the frequency counter, the connector pads «g»,»a»,»f»,»b» are not used because these four resistors R5..R8 are connected from the PIC board directly to the backside of the first seven-segment digit (see below). The letters on the left side are the segments. Use firmware «counter1.hex» for this circuit, and a 4-MHz crystal) The resistors R4..R11 set the brightness and the power consumption. If you find some suitable low-current displays, use 1 kOhm or even more. Four bridges (drawn in red colour below) must be soldered on the board before fitting the seven-segment displays. Hour Meters Ruggedness and reliability are featured in our hour meters.
The frequency counter makes the result positive before displaying it. Poll the ‘programming function’ input («RA5»). If this digital input is low, enter programming mode (not explained here). If not, go to step 1 to begin the next measurement. During this time, the display multiplexer keeps running. For this reason, the ‘single zero’ (if no input signal is present) is not displayed in the 5th, but in the fourth digit. Note: There may be more menu items than shown here, but the principle remains the same. Power consumption The prototype (with R4..R11 = 390 Ohm) drew an average supply current of 40 mA (with 5 low-efficiency digits). With high-efficiency or low-current displays this can be significantly reduced.